1. Field of the Invention
The present invention relates to a gas sensor placed in an exhaust system of an internal combustion engine and used for combustion control.
2. Description of the Prior Art
Gas sensors installed in an exhaust system of an internal combustion engine such as an automobile engine and used for combustion control include an O2 sensor, an air fuel ratio sensor, an NOx sensor, an HC sensor and the like. Elements built in these gas sensors include a cup-shaped gas sensor element comprising a cup-shaped solid electrolyte, and a laminated gas sensor element constituted by laminating ceramic sheets, electrodes and the like owing to limitations such as early activation or detection principles (e.g., Japanese Patent Application Publication No. H9-127050).
The gas sensor element provided in the gas sensor must be exposed to an exhaust gas for gas density measurement, while the gas sensor element must be protected against characteristic deterioration caused by poison of the exhaust gas or against an element crack caused by water splash. For such reasons, a cover is provided for covering the gas sensor element. The cover has gas passage holes on its side surface or the like to lead the exhaust gas into a measured gas room formed inside the cover.
Incidentally, it has conventionally been known that the constitution of the cover is contrived so that the flow velocity of the exhaust gas may not have an influence on an output of the gas sensor when the exhaust gas is led into the cover from the gas passage hole (Japanese Utility Model Publication (after examination) No. H3-4930).
Furthermore, it has been known that the constitution is contrived so that it may be difficult for water spattering through an exhaust pipe in which the gas sensor is provided to get inside the cover from the gas passage hole (Japanese Patent No. 2641346, Japanese Patent Application Publication No. H9-222416).
Still further, when the element is the laminated one, in some cases, a difference arises in a positional relation between a gas flow direction and a normal direction of the gas sensor element at the time of setting the gas sensor. In this case, the cover contrived to reduce the difference of response speeds (directionality) caused by setting state is also known (Japanese Patent No. 2653831). However, the covers of conventional constitutions present a problem of slowed response speed if the directionality or water coming in is reduced.
Further yet, another problem is that the difference of the response speeds (setting angle dependency) is large when the positional relation between an axial direction of the gas sensor element and the gas flow direction is different. For example, in Japanese Patent No. 2653831 mentioned above, the gas passage holes are disposed closer to a tip end side than a gas leading part of the gas sensor, so that a gas component desired to be detected needs to reach the measured gas room by using only turbulence diffusion. Therefore, the response speed is slowed down compared to the case of the cover having the constitution that leads the gas in by using a steady flow.
Further yet, in Japanese Utility Model Publication (after examination) No. H3-4930 mentioned above, because the flow of the measured gas inside an inner cover is not uniform, the directionality occurs in the response speed, causing the difference of the response speeds to be 10 ms or more. This makes a large difference of the characteristics depending upon the setting directions of the gas sensor, which might make it impossible to expect accurate gas density measurements. In Japanese Patent No. 2641346 mentioned above, because the gas passage hole is not provided in a bottom surface part of the inner cover, the amount of gas flowing into the inner cover is small, and the response speed is therefore slowed down. Further, as the flow in the inner cover is not uniform, the directionality emerges. Further, if the area of the gas passage hole is enlarged to increase the response speed, the element crack due to the water splash is more likely to occur, and moreover, when the element is heated by a heater to keep a constant temperature, there is a problem of increased power consumption.
Incidentally, in German Patent No. 19628423A1, the side surface of an outer cover does not have the gas passage holes, and it is designed to lead the gas that will flow into the inner cover from the gas passage hole provided on the bottom surface of the outer cover. However, because this gas passage hole is vertical to the gas flow, it has resistance to the gas inflow and poses a problem of the slowed response speed. Further, if a tip end portion of the element is set inclining to a downstream side of the exhaust gas flow, it raises a problem of the slowed response speed, and if it is set inclining to an upstream side, it raises a problem of deteriorated water splash resistance.
In both of German Patent No. 19628423A1 and German Patent No. 4436580A1, because the inner cover projects from the outer cover, the inner cover is exposed directly to the gas flow, and therefore the inner cover is cooled down. Since a radiant heat quantity from the gas sensor element is proportionate to the fourth power of the temperature of the inner cover, the power consumption increases when the inner cover is cooled down.
In Japanese Patent Application Publication No. H9-222416, since the bottom surface of the inner cover and the bottom surface of the outer cover are kept away, the exhaust gas that has got in from the gas passage hole on the side surface of the outer cover flows out from the gas passage hole on the bottom surface of the outer cover. This reduces the amount of gas flowing into the inner cover, and the response speed is thus slowed down.
In Japanese Patent Application Publication No. 2000-171429, if the tip end portion of the element is set inclining to the downstream side or the upstream side toward the flow of the exhaust gas, it raises a problem that responsiveness is slowed down. In other words, the setting angle dependency is increased, giving trouble in setting operation of the gas sensor.
The present invention has been made in view of such conventional problems, and is intended to provide a gas sensor with a high response speed, low power consumption, superior water splash resistance and a little setting direction dependency and setting angle dependency.
One aspect of the present invention is in a gas sensor comprising a gas sensor element and a cylindrical housing for inserting and fixing said gas sensor element, measured gas side covers having a bottom and provided on a tip end side of said housing and an atmosphere side cover provided on a base end side, wherein
said measured gas side covers comprises an inner cover for directly covering the gas sensor element and an outer cover directly exposed to measured gas ambience, and are provided with a measured gas room inside said inner cover;
gas passage holes for leading a measured gas into said measured gas room are provided on side surfaces of said inner cover and said outer cover respectively, and the gas passage hole provided on said outer cover is disposed in a position much closer to the tip end side than the gas passage hole provided closest to the tip end side in said inner cover; and
partitions disposed extendedly in an axial direction of the gas sensor are provided between said outer cover and said inner cover.
Next, functional effects of the present invention will be described. In the gas sensor in accordance with the present invention, the partitions disposed extendedly in an axial direction are provided between the outer cover and the inner cover, and consequently, it is possible to prevent the measured gas that has got in from the gas passage hole on the outer cover from passing other gas passage holes to flow out of the outer cover again, and further possible to rectify a gas flow between the outer cover and the inner cover so that the measured gas can quickly reach the gas passage hole on the inner cover along the partitions. In this way, since the measured gas can quickly reach the measured gas room inside the inner cover, it is possible to make the response speed of the gas sensor faster.
Furthermore, since the partitions function as guide plates of the measured gas, the measured gas can be led from the gas passage holes to the measured gas room always in the same state, without depending upon the setting direction and setting angle of the gas sensor.
Still further, the gas passage hole provided on the outer cover is disposed in a position much closer to the tip end side than the gas passage hole provided closest to the tip end side in the inner cover. This makes it possible to prevent the gas passage holes on the outer cover and those on the inner cover from being in a confronting state, and thus both the flow holes will be in a communicating state, thereby preventing water drops from getting in from the outside. This means that when the water drops get in from the gas passage hole of the outer cover, it is difficult for the water drops to reach the gas sensor element in the measured gas room by the blocking of the inner cover. In this way, the gas sensor in accordance with the present invention has high water splash resistance.
Further yet, as it is not necessary to enlarge the diameter of the gas passage holes to enhance responsiveness, the inflow amount of the gas can be controlled, and as heat taken away from the gas sensor element is reduced, it is possible to reduce the power consumption of the heater for heating the gas sensor element.
As described above, according to the present invention, it is possible to provide the gas sensor with the high response speed, low power consumption, superior water splash resistance and a little setting direction dependency and setting angle dependency.
Furthermore, in the gas sensor of the present invention, it is preferable that the gas passage holes to be provided in the outer cover and the inner cover satisfy the following requirements:
First, it is preferable that the gas passage holes to be provided on the side surfaces of the outer cover and the inner cover are each of the same shape. It is possible to equalize the inflow amount of the measured gas in each gas passage hole by making gas passage holes uniform, so that the dependency on the setting angle can be reduced.
Furthermore, it is preferable that two or more and eight or less gas passage holes are provided. In this way, the gas flows in equally from each hole, and the setting directionality can be reduced. Only one gas passage hole might cause the direction dependency, and if nine or more gas passage holes are provided, manufacturing costs of the covers might be increased.
Still further, it is preferable that the gas passage holes are provided at equal intervals in a circumferential direction of the cover. This can reduce the setting direction dependency.
Further yet, it is preferable that the above gas passage holes are arranged evenly at the same height in the axial direction. By arranging the gas passage holes evenly at the same height in the axial direction, it is possible to reduce the setting angle dependency and the setting direction dependency.
Further yet, in the gas sensor of the present invention, the gas sensor element can be applied to one that use a cup-shaped element (see FIG. 14) besides a laminated element, as shown in FIG. 1. However, by applying the present invention to the laminated element that is more fragile, the present invention functions more effectively.
Next, as one aspect of the present invention, it is preferable that the partitions are constituted in a way to project from the inner surface of the outer cover to the inner cover in the sectional diameter direction of the gas sensor. This makes it possible to prevent the measured gas that has got in from the gas passage hole on the outer cover from passing other gas passage holes to flow out of the outer cover again, and further possible to rectify the gas flow between the outer cover and the inner cover so that the measured gas can quickly reach the gas passage hole of the inner cover along the partitions. In this way, since the measured gas can quickly reach the measured gas room inside the inner cover, it is possible to make the response speed of the gas sensor faster.
Next, as one aspect of the present invention, it is preferable that the partitions are constituted in a way to project from the outer surface of the inner cover to the outer cover in the sectional diameter direction of the gas sensor. This integrates the partitions with the inner cover, thereby lowering the setting cost of the partitions.
Furthermore, the gas flow can be rectified between the outer cover and the inner cover so that the measured gas that has got in from the gas passage hole on the outer cover may be prevented from passing other gas passage holes to flow out of the outer cover again, and that the measured gas can quickly reach the gas passage hole of the inner cover along the partitions. In this case, since the measured gas can quickly reach the measured gas room inside the inner cover, it is possible to make the response speed of the gas sensor faster.
Next, as one aspect of the present invention, it is preferable that the projection height of the partitions is ⅓ or more of a clearance between the inner surface of the outer cover and the outer surface of the inner cover. This makes it possible to enlarge a component in an axial direction of the gas flow between the inner cover and the outer cover.
Furthermore, when the projection height is below ⅓ of the clearance, the component in the axial direction of the gas flow is not very large, which might result in insufficient rectification effects to retain the setting direction dependency and setting angle dependency.
The projection height is the distance between the inner surface of the outer cover and the inner surface of the partition. The clearance is the distance between the outer surface of the inner cover and the inner surface of the outer cover. Examples of these are indicated as a, b in the drawings of each Embodiment.
Next, as one aspect of the present invention, it is preferable that the axial length of the partitions is xc2xd or more of the axial length of the gas passage hole. This makes it possible to enlarge the component in the axial direction of the gas flow between the inner cover and the outer cover.
If the axial length is shorter than xc2xd, the measured gas might pass other gas passage holes to flow out of the outer cover again.
An upper limit of the axial length will be described later.
Next, as one aspect of the present invention, it is preferable that each of the partitions is provided between two adjacent gas passage holes made on the outer cover such that the partitions are circumferentially arranged. In this way, the gas flow can further be rectified between the outer cover and the inner cover, thereby making it possible to obtain more of the effects in accordance with the present invention.
Next, as one aspect of the present invention, it is preferable that the partitions are provided in the circumferential gaps communicating with the plurality of gas passage holes made on the outer cover, and that the axial length of the partitions is xc2xd or more of the axial length of the gas passage hole. This makes it possible to further rectify the gas flow between the outer cover and the inner cover, thereby allowing not only to obtain more of the effects in accordance with the present invention but also to enlarge the component in the axial direction of the gas flow between the inner cover and the outer cover. If the axial length is shorter than xc2xd, the measured gas might pass other gas passage holes to flow out of the outer cover again.
Next, as one aspect of the present invention, it is preferable that the partitions are constituted of concave parts made toward the inside in a sectional diameter direction on the side surface of the outer cover.
Furthermore, as one aspect of the present invention, it is preferable that the partitions are projections provided in the circumferential gaps communicating with the plurality of gas passage holes made on the side surface of the outer cover, and that these projections provide cuts on part of the side surface of the outer cover, and the partitions are constituted by bending the cut part. In this case, the partitions can be made integrally with the outer cover by applying punching-bending forming to the outer cover, thereby making it possible to reduce processing work and material costs.
Next, as one aspect of the present invention, it is preferable that an end portion of the partitions on the base end side in an axial direction of the gas sensor does not reach the gas passage hole provided on the inner cover. In this case, however relative positions of the inner cover and the outer cover in a diametric direction, which are rectangular to the axial direction of the gas sensor, may be determined, the flow of the measured gas is not obstructed and the responsiveness is difficult to get worse.
That is, the responsiveness hardly changes between the case where the outer cover is set to the inner cover at a predetermined angle and the case where the outer cover is set as a position at which the outer cover is rotated at an arbitrary angle from the predetermined angle above. Therefore, it is not necessary to determine the positional relations of the inner cover and the outer cover when both the covers are set, thereby making possible to lower setting cost.
If the end portion of the partitions on the base end side reaches the gas passage hole on the inner cover, in other words, since the end portion of the partitions on the base end side overlaps the gas passage hole on the inner cover, the responsiveness might get worse. In order to prevent this, it is necessary to contrive in such a way as to set the outer cover in a position not to obstruct the gas flow to the gas passage hole of the inner cover, which might increase the setting cost.
Next, as one aspect of the present invention, it is preferable that the gas sensor element is board-shaped, and that its sectional shape in a diametric direction of the inner cover is elliptic or square. This makes it possible to reduce not only the capacity in the inner cover but also the capacity of the measured gas room formed inside the cover. Thus, the responsiveness of the gas sensor can be enhanced.
Next, as one aspect of the present invention, it is preferable that the axial distance along the axial direction of the gas sensor between the gas passage hole provided closest to the tip end side on the inner cover and the gas passage hole provided closest to the base end side on the outer cover is 5 mm or more. This can prevent the water drops that have got in from the gas passage hole on the side surface of the outer cover from getting inside the cover from the gas passage hole of the inner cover. At this time, the water drops are discharged from the gas passage hole on the outer cover different from the gas passage hole through which the water drops has got into, or the water drops evaporate in the gap between the outer cover and the inner cover. If the axial distance is below 5 mm, the water drops that have got in from the gas passage hole of the outer cover get inside the inner cover, which might lead to the element crack caused by the water splash or the like.
Next, as one aspect of the present invention, it is preferable that the outer cover and the inner cover are in a shape having a bottom, and the distance between bottom surfaces of both covers are in a range of 0 to 5 mm. This can prevent the measured gas that has got in from the gas passage hole on the outer cover from directly getting out from an opening of the bottom surface, thereby allowing the response speed to be faster.
If the distance between the bottom surfaces exceeds 5 mm, the gas that has got in from the gas passage hole on the outer cover might directly get out from the opening of the bottom surface. The distance between the bottom surfaces is the distance between the inner surface of the outer cover and the outer surface of the inner cover.